Other network signal at 100%

Hi, in my wireless connection manager, it shows my network with a signal of between 50 and 60% and I have no problem connecting, but there is another wireless netork- not mine that shows 100% signal. My router is about 6 metres away from my PC and I live in a detached house where the nearest house is at least 12 meters away. Can any body expain this. Occasionally the same networks signal goes down to about 30%,but usually it's 100%. Are there very powerful routers?